Two major related problems are often associated with known hearing aids. These are feedback and poor physical fit or discomfort. Both of these problems may result in hearing aids being returned to the manufacturer to be remade or returned for credit.
If a hearing aid does not make a good seal in the ear, oscillation producing feedback usually occurs. This results in a device whose gain can not be turned up sufficiently to provide the user with the needed amplification.
A poor fit can be the result of, among other causes, sensitivity in the bony portion of the ear canal, an imperfect impression of the ear canal, variability in the shell manufacturing process, or ear anomalies such as bumps or birthmarks. A poor fit will reduce user satisfaction and promote a return or non-use of the instrument.
Hearing aids are conventionally tested by mounting each unit in putty and completely sealing it on a standard test coupler. The performance of the mounted unit is then measured. If the unit is within its specifications, it is then shipped to the customer.
If the hearing aid does not produce an adequate seal in the user's ear, the device's potential can not be achieved. Additionally, when the human jaw moves due to talking, chewing, etc., the shape of the ear canal changes. A rigid, conventional shell cannot adjust for the changes in ear canal shape due to movement of the jaw. Hence, an entirely rigid hearing aid shell that is perfectly fitted initially may produce unsatisfactory results in normal use.
Thus, there continues to be a need for hearing aid shells which can provide better seals than heretofore known. Preferably such improved seals could provide comfortable fit under both static and dynamic conditions of use.